Due to rapid innovation in the electronic communication technology, dual-band antenna system for use in a mobile phone is in the trend. Since the electronic communication apparatus is targeted to be in the compact size, it is the prime object of the manufacturer to produce and design the antenna system with dual bands within the limited space of the apparatus. The design and structure of the antenna system can affect the radiating efficiency and the quality of impedance matching in the feed line.
FIG. 1 shows a conventional antenna system used in a mobile phone. The conventional antenna system includes a helical coil having a plurality of turnings, a diameter D and a pitch distance S between the adjacent two turnings, wherein by making an appropriate adjustment in the diameter D with respect to the pitch distance S. The conventional antenna system is adapted to radiate radio signal in Normal Mode (where D<<λ) or Axial Mode (when π●D≧λ), in which λ denotes the wavelength of the operation frequency. Under the Normal Mode, a conventional wire serves as a Monopole Antenna once the diameter D is substantially equivalent to zero (D=0), the most effective radiating direction is in the plane perpendicular to the axial direction of the conventional wire. In case, the pitch distance S is substantially equivalent to zero (S=0), the conventional antenna system has a loop configuration, generally known as Loop Antenna.
Antenna efficiency and quality are achieved by minimizing resistance losses. Impedance is accumulated within small wire conductors used in the conventional antenna system. It is also noted that a RF connector must be employed in order to integrate the conventional antenna system (whether it has a Helix, Sleeve or Monopole design) within or outside a telecommunication apparatus (such as a mobile phone). Thus, an extra manufacture cost is consequently resulted when fabricating the conventional antenna system thereon.